1. Field of the Invention
The present invention relates to a rotary connector which establishes electrical connection using a flexible cable between a pair of housings coupled in a relatively rotational relation and, more specifically, to a lock mechanism for use in the rotary connector, for retaining both housings in their neutral rotational position until the rotary connector is mounted on the steering device of a vehicle.
2. Description of the Related Art
Some rotary connectors comprise a pair of rotating and stationary housings coupled in a relatively rotational relation, and a flexible cable coiled within an annular container defined between both housings, with both ends of the flexible cable supported respectively at both housings to be connected to external electrical connections. As the rotating housing rotates relative to the stationary housing, the flexible cable is coiled tightly or loosely within the container depending on the rotation direction of the rotating housing. In either movement, electrical connection between both housings is maintained via the flexible cable.
The rotary connector thus constructed is used as electrical connection means for an air bag inflator, a horn switch and the like, with the stationary housing mounted on a combination switch as a stator member of a steering device while the rotating housing mounted on a steering wheel as a rotor member of the steering device. The rotary connector is required to rotate in a balanced fashion from the neutral rotational position of the steering wheel with a range of travel in clockwise rotation and a range of travel in counterclockwise rotation being equal. For this reason, a known rotary connector is typically provided with a lock mechanism which retains both housings in the neutral position until the rotary connector is mounted onto the steering device.
One of known rotary connectors with a lock mechanism is a lock member of a synthetic resin into which a coupling portion, a finger-hook portion and a key portion are integrally formed, wherein a thin portion is formed between the coupling portion and the finger-hook portion. Using the lock member, the relative rotation of one housing to the other housing is blocked. More particularly, with both housings positioned at the neutral position, the coupling portion of the lock member is engaged with a coupling hole of one housing while the key portion is engaged with a rotation restraint portion of the other housing, and thus the free rotation of one housing to the other is restrained. Such a locked state is continuously maintained until the mounting of the rotary connector onto the steering device. When the rotary connector is mounted on the steering device, the finger-hook portion is drawn using a finger or a tool and then the finger-hook portion and the key portion are broken at the thin portion away from the coupling portion. The locked state of the housings by means of the lock member is thus released. In this unlocked state, the coupling portion broken at the thin portion remains in the coupling hole, and thus an unintentional removal of the lock member can be checked by the presence of the coupling portion.
In such a conventional rotary connector, the finger-hook portion and the coupling portion are arranged with the thin portion therebetween, generally in a line in alignment with the direction of drawing of the finger-hook portion. If the thin portion is designed to be mechanically too weak, it will be easily and possibly unintentionally ruptured in the locked state by an external force acting on the lock member and the housings. If the thin portion is designed to be strong enough to reliably maintain the locked state, the lock member is difficult to rupture when the releasing of the locked state is actually needed.